Modular apparatus for the demineralization of liquids

ABSTRACT

A modular sysTem for the demineralization of aqueous liquids comprising a plurality of modular units, each of the modular units being encapsulated and having a cathode proximate a first end of the modular unit and an anode proximate the opposite end of said modular, a plurality of alternating diluting compartments and concentrating compartments positioned between the cathode and the anode, and ion exchange material positioned within the diluting compartments. Each of the diluting compartments has a compartment spacer with an elongated central cavity and a plurality of fine slit openings at each end adjacent the cavity. The ion exchange means comprise a porous and permeable continuous phase of cation or anion exchange resin particles and a porous and permeable dispersed phase of clusters of the other of the cation or anion exchange resin particles. Releasable connecting means are provided to interconnect the modular units in the system to allow for facile substitution of modular units for servicing and to permit modification of flow capacity requirements by increasing or decreasing the total number of modular units in the system.

This application is a 371 of PCT/CA97/00088 filed, Feb. 10,1997.

FILED OF INVENTION

This invention relates to an apparatus for the demineralization ofliquids and, more particularly, relates to an apparatus comprised ofmodular units for the demineralization of liquids.

BACKGROUND OF THE INVENTION

The purification of liquid has become of great interest in manyindustries. In particular, pure water is used for many industrialpurposes rather than merely as drinking water. For example, pure wateris used in processes for producing semiconductor chips, in power plants,in the petro chemical industry and for many other purposes.

Ion exchange resins, reverse osmosis filtration and electrodialysistechniques have been used to reduce the concentration of particular ionsin a liquid.

Electrodeionization apparatus have recently been used with morefrequency to reduce the concentration of ions in a liquid. The term“electrodeionization” generally refers to an apparatus and a process forpurifying liquids which combine ion exchange resins, ion exchangemembranes and electricity to purify the liquids. An electrodeionizationmodule comprises alternating arrangements of cation permeable membranesand anion permeable membranes defining compartments therebetween. Inalternating compartments, there is provided ion exchange resin beads.Those compartments are known as diluting compartments. The compartmentswhich generally do not contain ion exchange resin are known as theconcentrating compartments. Ions migrate from the diluting compartmentsthrough ion exchange beads and ion permeable membranes into theconcentrating compartments by the introduction of current. The liquidflowing through the concentrating compartments is discarded or partiallyrecycled and the purified liquid flowing through the dilutingcompartments is recovered as demineralized liquid product.

Electrodialysis apparatus are similar in configuration toelectrodeionization apparatus. The main difference betweenelectrodialysis apparatus and electrodeionization apparatus is thatelectrodialysis apparatus do not use ion exchange resin to aid in theremoval of ions in the liquid passed through the diluting compartment.Often electrodialysis apparatus utilize membrane structures extendinginto the diluting compartments to aid in the removal of ions from aliquid.

There are two general configurations for electrodeionization andelectrodialysis apparatus: first, a plate and frame configuration, andsecond, a spiral-wound configuration.

U.S. Pat. No. 4,925,541 which issued May 15, 1990 to Giuffrida et al.discloses a plate and frame electrodeionization apparatus and method.The method for removing ions from a liquid in an electrodeionizationapparatus is carried out in an electrodeionization apparatus which has anumber of subcompartments in the diluting compartments. A mixture ofanion exchange resin and cation exchange resin is contained within thesubcompartments. The subcompartments are formed by a plurality of ribsextending along the length of the diluting or ion depletioncompartments.

U.S. Pat. No. 4,636,296 which issued Jan. 13, 1987 to Kunz disclosesanother embodiment of plate and frame apparatus and method for thedemineralization of aqueous solutions in which an aqueous liquid ispassed through alternating separate layers of cation exchange resin andanion exchange resin.

Plate and frame apparatus are large in size and typically suffer fromleaks because of the difficulty of sealing large vessels. Also, theunits often are oversize because of inflexibility in designing forcapacity, necessitating undesirably high capital and operating costs.

U.S. Pat. No. 5,376,253 which issued Dec. 27, 1994 to Rychen et al.discloses an apparatus for the electrochemical desalination of aqueoussolutions. The apparatus has a wound or spiral arrangement of anion andcation permeable membranes. Such apparatus are prone to leakage and arerelatively difficult to manufacture.

It is tedious to increase or vary the total output capacity of purifiedliquid for plate and frame configurations because it involvesdisassembly, insertion of additional ion permeable membranes, andinstallation of longer tie-bars to assemble the apparatus together. Itis also tedious if not impossible to increase or vary the total outputcapacity of purified liquid for spiral configurations because itinvolves disassembly and the insertion of a longer or shorterarrangement of anion and cation permeable membranes.

It is desirable to easily vary the total output capacity for pure liquidin apparatus for the demineralization of liquids. It is also desired tohave an electrochemical cell for electrodialysis and electrodeionizationapparatus which is relatively easy to situate in an existing watertreatment system.

SUMMARY OF THE INVENTION

The disadvantages of the prior art may be overcome by providing amodular system apparatus for the demineralization of liquids which has aplurality of modular units for the demineralization of liquids and whichis relatively easily assembled and disassembled for replacement ofmodular units or for increasing or decreasing design flow capacity byadding or deleting modular units in the system.

In its broad aspect, the apparatus for the demineralization of liquidsof the present invention comprises a plurality of modular units for thedemineralization of aqueous liquids arranged in parallel with the flowof a liquid and adapted to remove ions from the liquid. The apparatus isa modular system comprised of functional building blocks which can bereadily increased or decreased in size and volumetric capacity byincreasing or decreasing the number of these building blocks, i.e.modular units. Each of the modular units or cells has a cathode and ananode and means for applying an electrical voltage between the anode andthe cathode. A plurality of alternating diluting or demineralizingcompartments and concentrating compartments are positioned between thecathode and the anode. Ion exchange material is positioned within thediluting compartments and may be positioned within the concentratingcompartments. The apparatus has means for passing a first liquid to bepurified through the diluting compartments and means for passing asecond liquid through the concentrating compartments for accepting ionsfrom the first liquid. Each modular unit also has means for passing anelectrolyte to and from the cathode and anode, means for recovering thepurified liquid from the diluting compartments and means for removal ofthe concentrated liquid from the unit.

In another aspect of the invention, each of the modular units is anelectrodeionization apparatus. In another aspect of the invention, eachof the modular units is an electrodialysis apparatus. The modular unitsare in parallel with each other and have quick release securement meansto allow facile release of the modular units from the system.

In a preferred embodiment, the portable modular unit for use in amodular system for demineralizing aqueous liquids comprises a rigid,compact housing, said housing having a pair of opposite end plates, apair of opposite side plates, a top plate and a bottom plate, andconnector means for joining said end plates to the side and plates andfor securing the top and bottom plates thereto to form a liquid-tightencapsulating enclosure; said housing containing an anode compartmenthaving an anode and a cathode compartment having a cathode, a pluralityof cation exchange membranes and anion exchange membranes which arealternately arranged between the anode compartment and the cathodecompartment to form demineralizing compartments each defined by ademineralizing compartment spacer having an anion exchange membrane onthe anode side and by a cation exchange membrane on the cathode side,and concentrating compartments each defined by a concentratingcompartment spacer having a cation exchange membrane on the anode sideand by an anion exchange membrane on the cathode side, and a porous andpermeable ion exchanger filling said demineralizing compartments, andmeans for releasably connecting the modular unit to a piping system in amodular system whereby the modular unit can be removed from or added tothe modular system.

Each demineralizing compartment comprises a demineralizing compartmentspacer having an elongated central cavity for receiving the porous andpermeable ion exchanger, said spacer having a liquid inlet port at oneend and a liquid outlet port at the opposite end, a plurality of fineslit openings formed in the spacer at each end adjacent the cavity, andat least one channel in the spacer at each end for interconnecting theliquid inlet port to the fine slit openings adjacent the cavity and forconnecting the liquid outlet port to the fine slit openings, whereby anaqueous liquid can be flowed through the porous and permeable ionexchanger filling the demineralizing compartment. The ion exchangerpreferably a porous and permeable continuous phase of one of cationexchange resin particles or anion exchange resin particles and a porousand permeable dispersed phase of clusters of the other of the cationexchange resin particles or the anion exchange resin particles in thecontinuous phase.

Each of the end plates and the side plates of the modular unit has anouter surface and has a plurality of transverse upstanding reinforcingribs equispaced along the said outer surface formed integral therewith,and a cover plate substantially co-extensive with an attached to thedistal edges of the reinforcing ribs to form a rigid box structuretherewith for stiffening and reinforcing the plates from internalpressure.

Each said side plate has a socket formed integral therewith on the outersurface adjacent opposite side edges thereof as an extension of atransverse rib at each end thereof, each said socket having alongitudinal hole therein for loosely receiving a threaded bolt shankand a slot intersecting the hole adapted to receive a nut compatiblewith the threaded bolt shank, said slot having an interior shape such asa part hexagonal shape for receiving the nut in axial alignment with thebolt for threading the bolt into the nut.

Each said end plate has a boss formed on the outer surface adjacentopposite sides thereof at each end of a transverse rib, each said bosshaving a hole for receiving a bolt in alignment with a mating socket ina side plate.

The modular system for demineralizing aqueous liquids comprises aplurality of said portable modular units in which the portable modularunits are arranged in parallel, a piping system for feeding an aqueousliquid to be demineralized in parallel to the modular units and forremoving a demineralized aqueous liquid and a concentrated waste liquidin parallel from the modular units, means for applying an electricalvoltage between the anode and the cathode, and means for removablyconnecting the modular units to the piping system for facile adding of amodular unit to the system or removal of the modular unit from thesystem.

The apparatus of the invention provides a number of advantages includingthe following: 1. the electrical connections between the modular unitsallow for simple wiring of the apparatus; 2. the quick disconnection ofthe modular units enables the modular units to be easily serviced orreplaced; 3. the modular units simplify assembly and disassembly of theentire apparatus; 4. the relatively small size of the modular unitsallows for encapsulation of the units, thereby enhancing the integrityof the units and minimizing leakage; and 5. the total output capacity ofpurified liquid is easily increased or decreased to suit design flowrequirements by adding or removing modular units in a system assembly ofthe units.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view of a prior art electrodeionization 5apparatus;

FIG. 2 is a fragmentary sectional view taken along line 2—2 of FIG. 1;

FIG. 3 is a perspective view of an embodiment of the apparatus of theinvention for the demineralization of liquids; with a modular unitremoved for clarity of illustrations;

FIG. 4 is a perspective view of a preferred arrangement of ion exchangematerial of the invention;

FIG. 5 is a top plan view, partially in schematic, of the apparatus ofFIG. 3;

FIG. 6 is a perspective view of a second embodiment of the presentinvention;

FIG. 7 is a perspective view of the apparatus of FIG. 6 with a row ofmodules removed to more clearly show the liquid manifolds;

FIG. 8 is a sectional view, partly in elevation, of a manifold connectorembodiment of the invention shown in FIG. 6;

FIG. 9 is a perspective view of the housing of another embodiment of theinvention;

FIG. 10 is an exploded perspective view of the component of theembodiment shown in FIG. 9;

FIG. 11 is an enlarged perspective view of a preferred dilutingcompartment spacer of the invention shown in FIG. 10;

FIG. 12 is a perspective view of modular system of the invention showingthe stacks of modular units arranged in racks;

FIG. 13 is a perspective view of an embodiment of flow piping of theinvention;

FIG. 14 is a perspective view, partly cut away, of a side plate of themodule housing shown in FIG. 11; and

FIG. 15 is a perspective view, partly cut away, of an end plate of themodule housing shown in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a prior art plate and frame electrodeionizationapparatus 10 is shown whereby ions may be removed from a liquid. In thepreferred embodiment, ions such as sodium and chloride are removed fromwater.

The electrodeionization apparatus 10 has a rectangular frame 12. Theframe 12 comprises a rigid front plate 14 and a rigid back plate 16formed of metal. The front plate 14 and the back plate 16 are joinedtogether by a number of tie-bars or bolts 18. Each tie-bar 18 isinserted into a hole 20 located equispaced about the periphery of thefront plate 14 and inserted into corresponding holes 18 a in back plate16. A cathode depicted by numeral 22 (FIG. 2) is located proximate thefront plate 14 in a cathode compartment 23 and an anode depicted bynumeral 24 is located proximate the back plate 16 in an anodecompartment 25.

Openings 26 are located in the front plate 14 to allow liquid to enterthe electrodeionization apparatus 10 for treatment. Insulating electrodeblock 28 forming and electrode compartment abuts the perimeter of thefront plate 14 and insulating electrode block 30 forming an electrodecompartment continuously abuts the perimeter of the back plate 20. Theelectrodeionization apparatus 10 has a plurality of alternating cationpermeable membranes and anion permeable membranes depicted by numeral 32between the insulating electrode blocks 28 and 30. The cation permeablemembranes and anion permeable membranes 32 define the boundaries ofalternating concentrating and diluting compartments, to be described.

FIG. 2 shows representative concentrating compartments 44, 46 and arepresentative diluting compartment 48, between the concentratingcompartments, in further detail. Cation permeable membranes 36 and 38and anion permeable membranes 40 and 42 define the concentratingcompartments and diluting compartments. Spacers (not shown) are placedbetween the membranes in the diluting compartments and concentratingcompartments. The spacers in the diluting compartments 48 have openingsfor placement of ion exchange material such as ion exchange resin beads49. It will be understood that ion exchange resin may also be placedwithin the concentrating compartments.

FIG. 4 shows a preferred arrangement of ion exchange material of thepresent invention to be used within the diluting compartment 48 shown inFIG. 2. A bed 40 of porous and permeable continuous phase, i.e. matrix,of ion exchange material 50 has a plurality of spaced-apart cylinders ofporous and permeable clusters of second ion exchange material 52dispersed within matrix 50 transversely of the bed plane. The ionexchange materials 50 and 52 preferably are ion exchange resin particlesin the form of beads. The ion exchange material 50 and ion exchangematerial 52 exchange oppositely charged ions. For example, if continuousphase ion exchange material 50 is a cation exchange material, which willhave fixed negative charges to capture cations, dispersed phase ionexchange material 52 is an anion exchange material which will have fixedpositive charges to capture anions. The transverse arrangement ofclusters of the dispersed phased ion exchange material straddling orbridging the diluting compartments ensures that the aqueous liquid whichflows within the diluting compartments 48 comes into contact with bothforms of ion exchange resins to effectively exchange cations and anions.Referring to FIGS. 1, 2 and 4, aqueous liquid to be treated flowsthrough the openings 26 and through the concentrating compartments 44and 46 and the diluting compartment 48. Streams of liquid depicted byarrows 54 and 56 flow through the concentrating compartments 44 and 46respectively and a stream of liquid depicted by arrow 58 flows throughthe diluting compartment 48. The aqueous liquid contains ions such assodium and chloride ions.

Electric current flows between the cathode 22 in cathode compartment 23and the anode 24 in anode compartment 25. The current across cathode 22and anode 24 may be varied to control the overall efficiency of theelectrodeionization process.

As the liquid to be purified flows through the diluting compartment 48as depicted by arrow 58, it comes into contact with ion exchange resinbeads, as in the arrangement such as shown in FIG. 4. Cation exchangeresin 50 has fixed negative charges and captures cations such as sodiumions present in the liquid. Anion exchange resin 52 has fixed positivecharges and captures anions such as chloride ions present in the liquid.As the ion exchange takes place between the liquid to be purified andthe cation exchange resin beads 50 and the anion exchange resin beads52, the voltage induces the non-desired cations and anions typified bysodium ions and chloride ions respectively to travel through membranes38 and 40 and into the adjacent concentrating compartments 46 and 44.The ion exchange resin is disposed in a transverse arrangement relativeto the flow of liquid by arrows 53 as shown in FIG. 4. This arrangementensures that most of the liquid flowing through the diluting compartment48 comes into contact with ion exchange material 50 and 52.

In the preferred embodiment for purifing water, the current induces somesplitting of water into hydrogen and hydroxyl ions. The hydrogen ionsare transported through the cation exchange resin 50 towards the cationexchange membrane 38, and through cation exchange membrane 38 into theconcentrating compartment 46, as shown by arrows 66. The hydroxyl ionsare transported through the anion exchange resin 52, towards anionpermeable membrane 40, and through anion permeable membrane 40 into theconcentrating compartment 44, as shown by arrows 62. Thus, the ionexchange resin material 50 and ion exchange resin material 52 arecontinuously regenerated.

Anionic impurities, for example chloride ions in the water to bepurified in diluting chamber 48, are taken up by the anion exchangeresin material 52, by the usual ion exchange mechanism, and are thentransported along with hydroxyl ions through the anion exchange resin upto, and through anion permeable membrane 40, into concentratingcompartment 44 as shown by arrows 60. At the same time, an equivalentamount of hydrogen ions and impurity cations is transported from anadjacent diluting compartment into concentrating chamber 44, as shown byarrows 70.

Cationic impurities, for example sodium ions, in the water to bepurified in diluting chamber 48 are taken up by the cation exchangeresin material 50, by the usual ion exchange mechanism, and are thentransported along with the hydrogen ions through the cation exchangeresin up to, and through cation permeable membrane 38, intoconcentrating compartment 46 as shown by arrows 64. At the same time, anequivalent amount of hydroxyl ions and impurity anions is transportedfrom an adjacent diluting compartment into concentrating chamber 46, asshown by arrows 68.

The water flows through the concentrating compartments 44 and 46 to awaste tank (not shown) or is recycled. The purified water flowingthrough the diluting compartment 48 is recovered as product.

Referring now to FIGS. 3 and 5, the embodiment of the apparatus 74 ofthe present invention for the demineralization of a liquid such as watercomprises a plurality of either electrodeionization or electrodialysismodule units 76. In this embodiment, the modules 76 are arranged in aspaced-apart rows or racks 77 and 79.

Liquid to be treated flows through a feed conduit 80 in the direction asdepicted by arrow 82 (FIGS. 3 and 5) between module rows 77 and 79. Thefeed conduit has a number of lateral connector conduits 84 which allowthe liquid to flow in parallel into each of modules 76 in rows 77 and79. The flow of liquid from the feed conduit into the modules 76 isdepicted by arrows 86 in FIG. 5. At the same time, waste liquid flowsthrough a waste conduit 81 in the direction as depicted by arrow 83between rows 77 and 79 of modules 76. The waste conduit 81 has a numberof lateral connector conduits 85 which allow the liquid to flow inparallel into the modules 76 in the direction as depicted by arrow 87.

After the liquid has been purified in the modules 76 as described above,it flows out of the modules 76 in rows 77 and 79 in parallel as depictedby arrows 88 in FIG. 5 through lateral conduits 90 into a productcollection conduit 92. This is depicted by arrow 102 in FIG. 5. Wastefrom the diluting compartments flows out of modules 76 in parallelthrough conduits 96 shown by arrow 98 into a waste collection conduitfor flow as depicted by arrow 100.

An electrolyte is passed through the compartments which contain thecathode and the anode. The electrolyte flows through a conduit 104 andthrough a number of lateral connector conduits 106 from the modules 76in the rows 77 and 79 in the direction as depicted by arrows 108.

The modules in rows 77 and 79 preferably are separately electricallyfused.

FIGS. 6-8 show another embodiment of the apparatus 120 of the presentinvention. The apparatus 120 comprises a plurality of electrodionizationmodules or electrodialysis modules 122 arranged in rows 123 and 125.

FIG. 6 shows typical module 122 separated from the rack of modules.Module 122 has openings in one end plate 125 to allow for the flow ofliquid from the modules 122 to manifolds 130 and 132. Openings 134, 136and 138 allow for the streams of waste (concentrate), electrolyte andpurified liquid respectively to flow from the modules into respectiveconduits in manifold 130. Opening 140 allows for the introduction ofliquid to be purified and opening 142 permits introduction of liquid topick up waste (concentrate) liquid. The manifolds 130 and 132 haveconnectors 144 for connection to the modules 122.

With reference now to FIG. 8, connector 144 is a short pipe with o-ring146 which friction fits within the openings 134, 136, 138,140 and 142 ofthe module 122 and maintains a liquid seal with manifolds 130 and 132.FIG. 8 shows a cross-section of the manifold 130 which has conduits 148,150 and 152 corresponding to the flow of streams of purified liquid,electrolyte and waste, respectively.

FIGS. 9-15 show another embodiment of the modular unit of the apparatusof the present invention. With reference to FIGS. 9 and 10, anembodiment of module housing 160 is shown having side plates 162 and endplates 164 joined by a plurality of bolts 166. Top and bottom plates168, 170 seated into recesses in plates 168, 170 close the module. Thehousing plates are made of a material such as stainless steel or analuminum alloy configured in box-like structures to be described toprovide an assembly for a liquid-tight housing which encapsulates theinterior components. A PVC insulating electrode block 172 having inletand outlet pipes adjacent an end gasket 174 at one end houses a platinumcoated titanium anode 176 and a PVC insulating electrode block 178 atthe opposite end adjacent an end gasket 180 houses a stainless steelcathode 182. A polypropylene mesh electrode spacer 184, an electrodecompartment spacer 185 and a cation permeable membrane 186 are locatedat the anode end of the module. Next, a concentrating compartment spacer188 is adjacent an anion permeable membrane 190 which abuts ademineralizing or diluting compartment spacer 192 which houses ionexchange material i.e. ion exchanger 40, such as shown in FIG. 4.Spacers 188 and 192 may be injection molded polypropylene.

A plurality of diluting/concentrating pairs of compartments 196 comprisethe central portion of the module. A cation permeable membrane 198adjacent a concentrating compartment spacer 200, next to a cationpermeable membrane 202 and an electrode compartment spacer 204, abutstainless steel cathode 182.

FIG. 11 illustrates a diluent spacer 192 containing within a cavity 199defined by sides 201, 203 and ends 205, 206 an ion exchanger bed 40having continuous phase of ion exchange material 50 and discretespaced-apart cylinders or island clusters of a second ion exchangematerial 52, the cylinders 52 extending through bed 40 to be exposed onboth sides thereof. The discrete island or clusters 52 may be formedfrom a shallow bed or sheet of a continuous phase of ion exchange resinparticles of a first or second ion exchange material, preferably bondedby a polymeric binder, by die cutting clusters of the desired size andshape from the sheet. A sheet of a continuous phase of ion exchangeresin particles of an ion exchange material having an opposite chargebonded by a polymeric resin having a plurality of holes corresponding insize and shape to the clusters 52 die cut therefrom, can receive thecut-out clusters 52 having the opposite charge in tight-fittingfrictional engagement to form the ion exchangers. A thermoplasticpolymeric binder such as a low density polyethylene, linear low densitypolyethylene, or the like, in an amount sufficient to form a cohesivesheet or bed structure suitable for handling, while retaining goodporosity, liquid permeability and ion exchange capacity, can be used toform the starting sheets of the first and second ion exchange material.A liquid inlet port 208 is connected to cavity 198 by channels 210terminating in a plurality of fine slit openings 212, openings 212having a width smaller than the average size of the particles, e.g., ionexchange resin beads, which constitute the bed 40. The liquid dischargeport 214 is connected to cavity 198 by channels 216 and a plurality offine slit openings 218. Covers 220 close channels 210 and 216. Migrationof the resin material thus is inhibited and the resin material iseffectively contained within the diluent spacer during liquid flow.

FIG. 12 illustrates a typical rack of modular units 160 mounted in aframe 230. FIG. 13 shows the plumbing; conduit 232 for aqueous liquid tobe purified, conduit 234 for liquid to carry away impurities, conduit236 for purified liquid, conduit 238 for waste liquid and conduit 240for electrolyte. Junction boxes 242 provide the electrical connection tothe anodes and cathodes by wires 244, 246 (FIG. 12) individually fused.

Turning to FIG. 14, each side plate 162 is shown in more detail tocomprise inner planar wall 230 and a plurality of transverse upstandingreinforcing ribs 232, 234 equispaced along the length of plate 162 onthe outer surface 236 and formed integral therewith. Thin ribs 232 andthick central ribs 234 interconnect sockets 238, 240 formed at oppositeside edges 242, 244 of plate 162. A rectangular cover plate 246substantially co-extensive with and attached to the distal edges 248 ofribs 232, 234 forms a rigid box structure to effectively stiffen andreinforce side plate 162 from internal pressure.

Each of sockets 238, 240 comprises a slightly oversize hole 248 adaptedto receive the shank 250 of bolt 166 (FIG. 9) and a slot 252intersecting hole 248 adapted to receive a nut 254, typically ahexagonal nut, which is compatible with and receives bolt shank 250 inthreaded engagement. The interior of slot 252 is shaped to include foursides of hexagon to receive and to centre nut 254 in axial alignmentwith hole 248 and to prevent rotation of nut 254 to allow bolt shank 250to be threaded therein.

Each end plate 164, shown in more detail in FIG. 15, has transverseupstanding reinforcing ribs 260 equispaced along the length of the plateon the outer surface 262 formed integral therewith to interconnectbosses 264 having holes for receiving bolts 166. A rectangular coverplate 266 substantially co-extensive therewith and attached to thedistal edges 268 of ribs 260 forms a rigid box structure to effectivelystiffen and reinforce end plate 164 from internal pressure.

The plurality of bolts 166 tightened to the desired torque leveleffectively secures end plates 164 to side plates 162 and locks top andbottom plates 168 in inner wall slots to provide an encapsulated,liquid-tight housing capable of effectively withstanding internalpressures of 150 psig, or more without leakage of liquid.

The modular system of the present invention provides a number ofimportant advantages. The modular units are compact and can be carriedby two people for installation or replacement. The compact unitstypically are liquid tight and provide effective encapsulation. Thecompact size allows for facile replacement, obviating the need for fieldservicing. The parallel arrangement of units allows increase or decreaseof capacity by adding or deleting modular units. Failure of one unitdoes not shut down the system. Each configuration can be serviced bycommon piping, valves, pumps and the like for minimum capitalexpenditure and servicing costs. A system containing eight units, eachproducing nominally 12.5 U.S. gallons per minute (gpm), produces 100gpm. Stacking of eight units on top of eight units would doubleproduction to 200 gpm. Configurations of 100, 300 and 600 U.S. gpm andlarger are standard.

It will be understood, of course, that modifications can be made in theembodiment of the invention illustrated and described herein withoutdeparting from the scope and purview of the invention as defined by theappended claims.

We claim:
 1. A portable modular unit for use in a modular system fordemineralizing aqueous liquids comprising a rigid, compact housing(160), said housing having a pair of opposite end plates (164), a pairof opposite side plates (162), a top plate and a bottom plate (170), andconnector means (166) for joining said end plates (164) to the side andplates (162) and for securing the top and bottom plates (168, 170)thereto to form a liquid-tight encapsulating enclosure; said housing(160) containing an anode compartment having an anode (176) and acathode compartment having a cathode (182), a plurality of cationexchange membranes (186) and anion exchange membranes (190) which arealternately arranged between the anode compartment and the cathodecompartment to form demineralizing compartments each defined by ademineralizing compartment spacer (192) having an anion exchangemembrane (190) on the anode side and by a cation exchange membrane (186)on the cathode side, and concentrating compartments (196) each definedby a concentrating compartment spacer (200) having a cation exchangemembrane (198) on the anode side and by an anion exchange membrane (202)on the cathode side, each demineralizing compartment spacer (192) havingan elongated central cavity (199) for receiving porous and permeable ionexchanger (40), said spacer having a liquid inlet port (208) at one endand a liquid outlet port (214) at the opposite end, a plurality of fineslit openings (212, 218) formed in the spacer (192) at each end adjacentthe cavity (199), and at least one channel (210) in the spacer (192) ateach end for interconnecting the liquid inlet port (208) to the fineslit openings (212) adjacent the cavity (199) at one end and forconnecting the liquid outlet port (214) to the fine slit openings (218)adjacent the cavity (199) at the other end, whereby an aqueous liquidcan be flowed through the porous and permeable ion exchanger (40)filling the demineralizing compartment, a porous and permeable ionexchanger (40) filling said demineralizing compartments, said ionexchanger (40) consisting of a porous and permeable continuous phase(50) of one of cation exchange resin particles or anion exchange resinparticles and a porous and permeable dispersed phase of clusters (52) ofthe other of the cation exchange resin particles or the anion exchangeresin particles in the continuous phase (50), and means (144) forreleasably connecting the modular unit to a piping system in a modularsystem whereby the modular unit can be removed from or added to themodular system.
 2. A modular unit as claimed in claim 1 in which thefine slit opening (212, 218) have a width smaller than the average sizeof the cation or anion resin particles whereby migration of the resinparticles is inhibited during liquid flow.
 3. A modular unit as claimedin claim 1 in which each of the end plates (164) and the side plates(162) has an outer surface (236) and has a plurality of transverseupstanding reinforcing ribs (232, 234) equispaced along the said outersurface (236) formed integral therewith, and a cover plate (246)substantially co-extensive with an attached to the distal edges (248) ofthe reinforcing ribs (232, 234) to form a rigid box structure therewithfor stiffening and reinforcing the plates (164) from internal pressure.4. A modular unit as claimed in claim 3 in which each said side plate(162) has a socket (238, 240) formed integral therewith on the outersurface adjacent opposite side edges thereof as an extension of atransverse rib (232, 234) at each end thereof, each said socket (238,240) having a longitudinal hole (248) therein for loosely receiving athreaded bolt shank (250) and a slot (252) intersecting the hole (248)adapted to receive a nut (254) compatible with the threaded bolt shank,said slot (252) having an interior shape for receiving the nut (254) inaxial alignment with the bolt (250) for threading the bolt into the nut.5. A modular unit as claimed in claim 4 in which each said end plate(164) has a boss (264) formed on the outer surface adjacent oppositesides thereof at each end of a transverse rib (260), each said boss(264) having a hole for receiving a bolt (166) in alignment with amating socket (238, 240) in a side plate (162).
 6. A modular system fordemineralizing aqueous liquids comprising a plurality of portablemodular (160) units as claimed in claim 1, 2, 3, 4 or 5 in which saidportable modular units are arranged in parallel, a piping system forfeeding an aqueous liquid to be demineralized (232) in parallel to themodular units (160) and for removing demineralized aqueous liquid (236)and a concentrated waste liquid (234) in parallel from the modular units(160), means (242) for applying an electrical voltage between the anodeand The cathode, and means (144) for removably connecting the modularunits (160) to the piping system for facile adding of a modular unit(160) to the system or removal of the modular unit (160) from thesystem.
 7. A modular system as claimed in claim 6 in which the means forremovably correcting the modular units is a quick release securementmeans (144).
 8. A portable modular unit for use in a modular system fordemineralizing aqueous liquids comprising a rigid, compact housing(160), said housing having a pair of opposite end plates (164), a pairof opposite side plates (162), a top plate and a bottom plate (170), andconnector means (166) for joining said end plates (164) to the sideplates (162) and for securing the top and bottom plates (168, 170)thereto to form a liquid-tight encapsulating enclosure; said housing(160) containing an anode compartment including an anode (176) and acathode compartment including a cathode (182), a plurality of cationexchange membranes (186) and anion exchange membranes (190) which arealternately arranged between the anode compartment and the cathodecompartment to form demineralizing compartments each defined by ademineralizing compartment spacer (192) including an anion exchangemembrane (190) on the anode side and a cation exchange membrane (186) onthe cathode side, and concentrating components each defined by aconcentrating compartment spacer (200) including a cation exchangemembrane (198) on the anode side and by an anion exchange membrane (202)on the cathode side, and a porous and permeable ion exchanger (40)filing said demineralizing components, and means (144) for releasablyconnecting the modular unit to a piping system in a modular systemwhereby the modular unit can be removed from or added to the modularsystem.
 9. A modular unit as claimed in claim 8 in which eachdemineralizing compartment comprises a demineralizing compartment spacer(192) including an elongated central cavity (199) for receiving theporous and permeable ion exchanger (40), said spacer (192) including aliquid inlet port (208) at one end and a liquid outlet port (214) at theopposite end, a plurality of fine slit openings (212,218) formed in thespacer (192) at each end adjacent the cavity (199), and at least onechannel (210) in the spacer at each end for interconnecting the liquidinlet port (208) to the fine slit openings (212, 218) adjacent thecavity (199) and for connecting tee liquid outlet port (214) to the fineslit openings (212,218), whereby an aqueous liquid can be flowed throughthe porous and permeable ion exchanger (40) filling the demineralizingcomponent.
 10. A modular unit as claimed in claim 9 in which the fineslit opening (212,218) include a width smaller than the average size ofthe cation or anion resin particles whereby migration of the resinparticles is inhibited during liquid flow.
 11. A modular unit as claimedin claim 8 in which each of The end plates (164) and The side plates(162) includes a surface (236) including a plurality of transverseupstanding reinforcing ribs (232,234) equispaced along the said outersurface (236) formed integral therewith.
 12. A modular unit as claimedin claim 8 in which each of the end plates (164) and the side plates(162) includes an outer surface (236) and includes a plurality oftransverse upstanding reinforcing ribs (232, 234) equispaced along thesaid outer surface (236) formed integral therewith.
 13. The modular unita claimed in claim 12 in which each of the end plates (164) and the sideplates (162) include a cover plate (246) substantially co-extensive withand attached to the distal edges (248) of the reinforcing ribs (232,234) to form a rigid box structure therewith.
 14. The modular unit asclaimed in claim 12 in which each said side plate includes a socketformed integral Therewith on the outer surface adjacent opposite sideedges thereof, each said socket including a longitudinal hole thereinfor loosely receiving a thread bolt shank and a slot intersecting Thehole adapted to receive a nut compatible with the threaded bolt shank,said slot having an interior shape for receiving the nut in axialalignment with the bolt for Threading the bolt into the nut.
 15. Themodular unit as claimed in claim 14 in which each said end plateincludes a boss formed on the outer surface adjacent opposite sidesthereof at each end of a transverse rib, each said boss including a holefor receiving a bolt in alignment with the mating socket in a sideplate.
 16. A modular unit as claimed in claim 8 in which each said sideplate (162) includes a socket (238, 240) formed integral therewith onthe outer surface adjacent opposite side edges thereof.
 17. The modularunit as claimed in claim 16 in which each said socket includes alongitudinal hole (248) therein for loosely receiving a threaded boltshank (250) and a slot (252) intersecting the hole (248) adapted toreceive a nut (254) compatible with the threaded bolt shank (250), saidslot (252) including an interior shape for receiving the nut (254) inaxial alignment with the bolt (250) for threading the bolt (250) intothe nut (254).
 18. A modular unit as claimed in claim 17 in which eachsaid end plate (164) includes a boss (264) formed on the outer surfaceadjacent opposite sides thereof at each end of a transverse rib (260),each said boss (264) includes a hole for receiving a bolt (166) inalignment with a mating socket (238, 240) in a side plate (162).
 19. Themodular unit as claimed in claim 16 in which each said end plate (164)includes a boss (264) including a hole (248) for receiving a bolt (250)in alignment with a mating socket (238, 240) in a side plate (162).